1. Field of the Invention
The present invention relates to a thermally enhanced package for a semiconductor chip and a method of forming the same. It includes, but is not limited to, a package with an integrated heat sink for ball grid arrays (PBGAs and FBGAs), multi chip modules (MCMs) and quad flat nonleaded packages (QFNs).
2. Description of the Related Art
The quest to increase functionality and chip speeds is a continuous ongoing effort by every chip designer in the Semiconductor industry. The increase in signal speeds in the chips poses considerable challenges for thermal management. Higher signal speeds and higher functionality leads to higher junction temperatures. To keep the junction temperatures low, various thermal solutions are available.
Plastic Ball grid array (PBGA) packages are encapsulated individually. Therefore, one thermal solution is a drop-in heat sink that is embedded during encapsulation. However, drop-in heat sinks take-up space within the package, posing constraints in the placement of active chips and other devices. For example, FIG. 2 shows a cross-sectional view of a PBGA package that includes a drop-in heat sink 4.
Highly mass produced laminate based packages such as fine pitch BGAs (FBGAs), are arrayed and are molded in panel form and singulated to produce individual FBGA packages. Arrayed packages don't allow space for individual drop-in heat sinks and it is not economical to waste substrate real estate to have individual drop-in heat sinks for FBGA. Therefore, some approaches to deal with thermal management include the use of arrayed heat sinks with connecting down sets. However, these types of heat sinks have quality issues such as mold flash during the molding process. These quality issues lead to both aesthetic and as well as thermal performance problems.
Other known methods of incorporating heat sinks into packages also have several disadvantages. For example, they include multiple process steps which increase production time and costs. In addition, the heat sinks can be misaligned. Also, heat sinks can be easily peeled-off.
One of the current methods of producing a thermally enhanced semiconductor package is by attaching the heat sink 1 onto top surface of the fully molded semiconductor package by means of an adhesive layer 3 as shown in FIG. 1. However, this method provides an inconsistent adhesive coverage when the heat sink is attached, which might lead to easy removal of the heat sink. Other issues encountered with this method include controlling the amount of adhesive 3 needed to attach the heat sink 1 to the molded surface 2. Excessive adhesive 3 can cause bleed out, which ultimately contaminates the package edges or the contact pads. Insufficient adhesive coverage can also cause large gaps that adversely affect thermal performance. Finally, attaching heat sink 1 after singulation is not economically viable considering the mass scale production requirements of the package.
One object of the present invention is to provide a method of packaging an embedded heat sink semiconductor package whereby the semiconductor package has good thermal characteristics and can be assembled with a simple manufacturing process.
Another object of the present invention is to provide a heat sink structure that provides a vertical cushioning effect during molding.
Another object of the present invention is to provide a heat sink structure that created a lifting force that keeps the heat sink structure engaged with the release film during molding.
Another object of the present invention is to provide a heat sink structure that inhibits mold flash on the heat sinks.
Another object of the present invention is to provide a package that includes a notch of encapsulant around the corner of the package to act as an interlock for the heat sink, enhancing the holding strength between the heat sink and cured encapsulant.
Some of the innovativeness of this package is that it can be applied to any arrayed, lead frame based or laminate based packages which are molded on one side of the substrate. The heat sink can be any thermally conductive material (for example, copper).